Oakland Schools Chemistry Resource Unit
Bonding Jennifer Novak Andover High School Bloomfield Hills School District Bonding
Content Statements:
C3.2x Enthalpy
Chemical reactions involve breaking bonds in reactants (endothermic) and forming new
bonds in the products (exothermic). The enthalpy change for a chemical reaction will
depend on the relative strengths of the bonds in the reactants and products.
C4.4x Molecular Polarity
The forces between molecules depend on the net polarity of the molecule as
determined by shape of the molecule and the polarity of the bonds.
C5.5x Chemical Bonds - Trends
An atom’s electron configuration, particularly of the outermost electrons, determines
how the atom can interact with other atoms. The interactions between atoms that hold
them together in molecules or between oppositely charged ions are called chemical
bonds.
C5.5x Chemical Bonds
Chemical bonds can be classified as ionic, covalent, and metallic. The properties of a
compound depend on the types of bonds holding the atoms together.
C4.3x Solids
Solids can be classified as metallic, ionic, covalent, or network covalent. These different
types of solids have different properties that depend on the particles and forces found
in the solid.
Content Expectations:
C3.2b - Describe the relative strength of single, double, and triple covalent bonds
between nitrogen atoms.
C4.4b - Identify if a molecule is polar or nonpolar given a structural formula for the
compound.
C5.5A - Predict if the bonding between two atoms of different elements will be primarily
ionic or covalent.
C5.5c - Draw Lewis structures for simple compounds.
C5.5d - Compare the relative melting point, electrical and thermal conductivity, and
hardness for ionic, metallic, and covalent compounds.
C5.5e - Relate the melting point, hardness, and electrical and thermal conductivity of a
substance to its structure.
C4.3e - Predict whether the forces of attraction in a solid are primarily metallic,
covalent, network covalent, or ionic based upon the elements’ location on the periodic
table.
Background Information:
An easy way to determine whether a compound will be ionic or covalent is the
electronegativity of its substituent elements. Electronegativity is a measure of how
much an element wants to pull electrons away from an element that it has bonded to.
Chemical compounds in which the two elements have very different electronegativities
are ionic, because the element with a higher electronegativity pulls valence electrons
completely off the less electronegative element. Chemical compounds in which the two
elements have similar electronegativities are covalent, because neither atom gives up
its electrons.
COVALENT BONDING: Valence electrons are equally shared between the bonded
atoms of nonmetallic elements.
POLAR COVALENT BONDING: Electrons are shared but NOT equally between
atoms of nonmetallic elements. Many compounds have the characteristics of
BOTH ionic and covalent bonding. Electronegativity differences determine the
balance of character. Example: water, carbon dioxide
In NONPOLAR COVALENT BONDING: Electrons are shared equally between
two atoms that are exactly the same from nonmetallic elements. Example:
hydrogen gas
IONIC BONDING: Valence electrons are completely transferred from one atom to the
other atom of metallic elements. Ionic bonds occur between metals and nonmetals
when there is a large difference in electronegativity. Example: salts
METALLIC BONDING: Valence electrons are shared among all of the atoms of
metallic elements. Metallic bonding occurs when metals bond to either themselves or
mixed with other metals in alloys. Example: iron, magnesium
Another way to determine the type of bonding between elements is by the location of
the elements on the periodic table. Looking at the formula of the substance, if the
elements are a mix of metals and nonmetals it is an ionic compound. A compound
containing only nonmetals is covalent, and only metals is metallic.
The reason why atoms bond can be explained by the octet rule, which states that
atoms will acquire eight valence electrons (the outermost electrons) to become stable.
When atoms become more stable, they lower in energy.
Properties of Ionic, Covalent, and Metallic Compounds
Ionic Compounds
-Formed from a
combination of metals and
nonmetals.
-Electron transfer from the
cation to the anion.
-Opposite charged ions
attract each other.
Solids at room temperature
Covalent Compounds
-Formed from a
combination of nonmetals.
-Electron sharing between
atoms.
Metallic Compounds
-Formed from a
combination of metals
-“sea of electrons”;
electrons can move
among atoms
High melting points
Can be solid, liquid, or gas
at room temperature.
Low melting points
Solids at room
temperature
Various melting points
Dissolve well in water
Do not dissolve in water
Conduct electricity only
when dissolved in water;
electrolytes
Brittle, hard
Do not conduct electricity;
nonelectrolytes
Do not dissolve in water.
(Sugar is an exception)
Conduct electricity in solid
form.
Soft
Metallic compounds range
in hardness. Group 1 and
2 metals are soft;
transition metals are hard.
Metals are malleable,
ductile, and have luster.
*MOST compounds are a mixture between ionic and covalent
Drawing Lewis Structures for Covalent Compounds
1. Determine the number of valence electrons available in the atoms to be
combined. (Number of atoms of each element • number of valence electrons)
2. Arrange the atoms to form a skeleton structure for the molecule. If carbon is
present, it is the central atom. Otherwise, the least electronegative atom is
central (except for hydrogen, which is never central). Connect the atoms by
bonds. Remember that a dash represents two electrons.
3. Add remaining electrons as unshared pairs of electrons to each nonmetal atom
(except hydrogen) so that each is surrounded by eight electrons.
4. Count the electrons in the Lewis structure to be sure that the number of valence
electrons drawn in the structure equals the number of available valence
electrons.
a. Check to see that each atom has eight valence electrons. If not, move
lone pairs in order to make double or triple bonds between non-hydrogen
atoms until the outer shells of all atoms are completely filled.
Changes in Potential Energy in the Bonding Process
Changes in Potential Energy in the Bonding Process - Continued
Terms and Concepts
Chemical Bond
Covalent Bond
Ionic Bond
Metallic bond
Bond Length
Double and Triple Bond
Electron sharing
Electron transfer
Ion
Polarity
Nonpolar bond
Polar bond
Potential energy
Intramolecular Force
Electronegativity
Dipole
Bond Energy
Hybridization
Molecular Geometry
Valence Shell Electron Pair
Repulsion
Websites and Resources for Bonding
Chemical Bonding Web quest
http://nths.newtrier.k12.il.us/academics/faculty/gressel/mendelevwebquest/
Flash Animation for Ionic vs. Covalent Bonding
http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/bom1s2_11.swf
VSPER Practice Problems
http://www.chem.purdue.edu/gchelp/vsepr/cmp2.html
Practice “flashcards” for naming/formulating ionic compounds
http://jchemed.chem.wisc.edu/JCEDLib/WebWare/collection/open/JCE2005WWOR002/n
om/nom1.html
VSEPR 3-D Models of Molecular Shapes
http://www2.wwnorton.com/college/chemistry/gilbert/tutorials/chapter_07/vsepr/index.
html
IM Forces and Phase Diagram – Flash Tutorial
http://www.wwnorton.com/college/chemistry/gilbert/tutorials/ch9.htm
H-Bonding (water) - Flash
http://www.northland.cc.mn.us/biology/Biology1111/animations/hydrogenbonds.html
Tutorials for Bonding Concepts (see details below)
http://www2.wwnorton.com/college/chemistry/gilbert/tutorials/ch7.htm
Section 7.3 Expanded Valence Shells (p. 343-347)
Explore the exceptions to the octet rule, and learn to identify the conditions
under which an element will expand its outer electron shell to hold more than 8
electrons. Includes practice exercises.
Section 7.6 VSEPR Model (p. 354-363)
This unit presents interactive three-dimensional representations of all the
molecular geometries, as well as chemical examples of each. . Simply click and
drag a molecule to rotate it in space.
Section 7.7 Hybridization (p. 363-371)
This tutorial animates the formation of hybrid orbitals from individual s and p
orbitals, shows examples of their geometry, and describes how they can produce
single, double, and triple bonds.. Includes practice exercises.
Bonding Unit
Activity #1: We’re Rich! Changing Pennies into Gold
Questions:
How do metals bond together?
What is an alloy?
Objectives:
To investigate metallic bonding.
Teacher Background Information
Physical Properties of Metals
Metals, although distinct from one another, share certain similarities that enable us to
classify them as metallic. A fresh metal surface has a characteristic luster. In addition,
metals that we can handle with bare hands have a characteristic cold feeling related to
their high heat conductivity. Metals also have high electrical conductivities; electrical
current flows easily through them. The heat conductivity of a metal usually parallels its
electrical conductivity. For example, silver and copper, which possess the highest
electrical conductivities, also possess the highest heat conductivities. This observation
suggests that the two types of conductivity have the same origin in metals, which we
will soon discuss.
Most metals are malleable, which means that they can be hammered into thin sheets,
and ductile, which means that they can be drawn into wires. These properties indicate
that the atoms are capable of slipping with respect to one another. Ionic solids or
crystals of most covalent compounds do not exhibit such behavior. These types of solids
are typically brittle and fracture easily. Consider, for example, the difference between
dropping an ice cube and a block of aluminum metal onto a concrete floor.
Electron-Sea Model for Metallic Bonding
Most metals form solid structures in which the atoms are arranged as closely packed
spheres. For example, each copper atom is in contact with 12 other copper atoms. The
number of valence electrons available for bond formation is insufficient for a copper
atom to form an electron-pair bond to each of its neighbors. If each atom is to share its
bonding electrons with all its neighbors, these electrons
must be able to move from one bonding region to
another.
The electron-sea model for metallic bonding cannot
adequately explain all of the properties of metals. It is,
however, a very simple model that can account for most
of the important characteristics of metals. In this model
the metal is pictured as an array of metal cations in a "sea" of valence electrons, as
illustrated in the figure. The electrons are attracted to the metal by electrostatic
attractions to the cations, and are uniformly distributed throughout the structure.
However, the electrons are mobile, and no individual electron is confined to any
particular metal ion. When a metal wire is connected to the terminals of a battery,
electrons flow through the metal toward the positive terminal and into the metal from
the battery at the negative terminal.
The high heat conductivity of metals is also accounted for by the mobility of the
electrons, which permits ready transfer of kinetic energy throughout the solid. The
ability of metals to deform (their malleability and ductility) can be explained by the fact
that metal atoms form bonds to many neighbors. Changes in the positions of the atoms
brought about in reshaping the metal are partly accommodated by a re-distribution of
electrons.
Transition Metals
Many of the most important metals of modern society are transition metals. Transition
metals, which occupy the d block of the periodic table, include such familiar elements
as chromium, iron, nickel, copper, silver and gold. Transition metals are commonly used
for the fabrication of items and construction of buildings. Additionally, many of them are
required in trace amounts for proper biological function. These include iron,
manganese, zinc, cobalt and copper. Transition metals owe their location in the periodic
table to the filling of the d subshells. The existence of these d electrons is partially
responsible for several characteristics of transition metals:
• They often exhibit more than one stable oxidation state.
• Many of the transition metal compounds and solutions containing transition
metal ions are colored. For example, solutions containing Cu+2 are blue, Fe+3 are
yellow and Ni+2 are green.
• Transition metals and their compounds exhibit interesting magnetic properties.
Electron Configurations and Oxidation States of the Transition Metals
When transition metals are oxidized (become positively charged ions) they lose their
outer s electrons before they lose electrons from the d subshell. For example, the
electron configuration of Fe is [Ar]3d64s2, whereas that of Fe+2 is [Ar]3d6. Formation of
Fe+3 requires the loss of one 3d electron, giving [Ar]3d5. Most transition-metal ions
contain partially occupied d subshells. The +2 oxidation state, which commonly occurs
for nearly all of these metals, is due to the loss of their two outer 4s electrons. This
oxidation state is commonly found for all these elements except Sc, where the +3 ion
with an [Ar] configuration is particularly stable. Oxidation states above +2 are due to
successive losses of 3d electrons. The maximum oxidation states of the transition
metals range from +2 to +8. In general, the maximum oxidation states are found only
when the metals are combined with the most electronegative elements.
Color
The color of transition metals is due to the presence of partially filled d orbitals. In an
isolated atom, all five of the d orbitals are equivalent in energy. When the atom is
surrounded by solvent molecules or anions, the varying shape of the d orbitals (recall
that two of the d orbitals have a shape different than the other three), cause them to
have slightly different energies. The difference in energy between the levels
corresponds to the energy of visible light. The metal complex is therefore able to
absorb photons of visible light. When it does so, an electron jumps from a lower energy
d orbtial to a higher energy d orbital and the solution will appear to be the
complementary color of the light absorbed. For example, a copper ion in aqueous
solution is surrounded by six water molecules. This results in two sets of d orbitals that
are different in energy by about 3.2 x 10-19 joules. A photon of light that has this energy
can be absorbed causing an electron to be excited from one of the lower energy levels
to one of the higher energy levels. Since the absorbed photon has a wavelength of
620 nm, orange light is being absorbed, and the solution appears to be orange's
complementary color which is blue.
Magnetism
The strongest form of magnetism is called ferromagnetism. Ferromagnetism arises
when the unpaired electrons of the atoms or ions in a solid are influenced by the
orientations of the electrons of their neighbors. The most stable (lowest energy)
arrangement results when the spins of electrons on adjacent atoms or ions are aligned
in the same direction. When a ferro magnetic solid is placed in a magnetic field, the
electrons tend to align strongly along the magnetic field. When the external magnetic
field is removed, the interactions between the electrons cause the solid as a whole to
maintain a magnetic moment. We then refer to it as a permanent magnet. The most
common examples of ferromagnetic solids are the elements Fe, Co, and Ni. Many alloys
exhibit greater ferromagnetism than do the pure metals themselves. Some metal oxides
(for example CrO2 and Fe3O4) are also ferromagnetic. Several ferromagnetic oxides are
used in magnetic recording tape and computer disks.
Alloys
An alloy is a material that contains more than one element and has the characteristic
properties of metals. Alloying is important because it is one of the primary ways of
modifying the properties of pure metallic elements. As an example, pure gold is too soft
to be used in jewelry, whereas alloys of gold and copper are quite hard. Pure gold is
termed 24 karat; the common alloy used in jewelry is 14 karat, meaning that it is 58
percent gold (14/24 x 100%). A gold alloy of this composition has suitable hardness to
be used in jewelry. Other examples are given below. In this lab, heating the penny
fuses the zinc and copper to form an alloy called brass. Brass is a homogeneous metal
that varies from 60-82% Cu and from 18-40% Zn. Brass has a relatively low melting
point, so the coating can be destroyed by heating the penny for too long.
Name of Alloy
Yellow Brass
Steel
Stainless steel
Plumber’s solder
Sterling silver
Dental amalgam
Composition by Mass
67% Cu, 33% Zn
97% Fe, 3% C
80.6% Fe, 0.4% C, 18%
Cr, 1% Ni
67% Pb, 33% Sn
92.5% Ag, 7.5% Cu
70% Ag, 18% Sn, 10% Cu,
2% Hg
Examples
Hardware Items
Steel chain, tools
Tableware
Soldering Joints
Tableware
Dental fillings
Copper: A Coinage Metal
Copper is sometimes found in metallic form in nature and evidence suggests that such
naturally occurring copper was used during the Stone Age. As early as 10,000 years
ago, (8000 B.C.), the metal was hammered into items such as coins, jewelry, tools, and
weapons. About 3800 B.C. the discovery was made in the Middle East that bronze
formed when tin combined with copper, thus starting the Bronze Age. The discovery
was likely accidental, occuring during the reduction of copper ore in a wood fire while
some tin ore was present. The advantage of bronze is that it is sufficiently hard to keep
a cutting edge, something that copper cannot do. Because of its properties, all early
civilizations that produced bronze used it to create weapons as well as exquisite works
of art. Brass is an alloy made of varying proportions of copper and zinc (20 to 45% Zn),
which becomes harder as the percentage of zinc increases. Because it is easy to forge,
cast, and stamp, brass is widely used for pipes, valves, and fittings.
Copper is used in all U.S. coins. By 1982, the price of copper rose to where it was
costing the U.S. Treasury Department more than 1 cent to make a penny. Since then,
to conserve copper and reduce costs, the penny has been made of 97.5% zinc and
2.5% copper, with the zinc core sandwiched between two thin layers of copper. The
silver-colored coins actually contain no silver. The nickel is made of a copper (75%) and
nickel (25%) alloy of uniform composition throughout the coin. The other silvercolored
coins are a "sandwich" made of a pure copper core covered with a thin layer of a
copper and nickel alloy (91.67% copper).
Sources:
Procedure taken from: Szczepankiewicz, S. H., Bieron, J.F. and Kozik, M. The "Golden
Penny"
Demonstration: An Explanation of the Old Experiment and the Rational Design of the
New and Simpler Demonstration. J. Chem. Educ. 1995 72 386.
The background material was modified from:
Moore, J.W., C.L. Stanitski and P.C. Jurs Chemistry: The Molecular Science Brooks/Cole,
Australia, 2002.
Brown, T.L., H.E. LeMay and B.E. Bursten Chemistry: The Central Science Prentice
Hall, 8th edition, New Jersey, 2000.
Lab: Preparation of "Gold" Pennies
Materials:
Granular zinc
3 M NaOH
Evaporating dish
Tongs
Hot plate
Safety Concerns:
Use granular zinc, not powdered zinc or zinc dust. Sodium hydroxide is caustic – Use
care when heating and handling this solution. Safety glasses and a lab apron MUST be
worn. Avoid contact of all chemicals with eyes and skin. The granular zinc can be
rinsed with water and used again for this lab. Consult MSDS for any additional safety,
handling, and disposal information.
Pre-lab Procedure Check Questions
a. In order to make the silver colored penny; the penny is placed in an evaporating dish
containing what solution and what solid material?
b. What will you use to heat the silver colored penny?
c. How should you heat the silver penny (strongly or gently)?
Procedure
Pair up with someone. While each person should prepare their own pennies, the two
people can both use the same evaporating dish and zinc.
1. Place ~2 g of granular zinc in an evaporating dish on a hot plate set to medium high.
2. Add ~ 20 ml of 3 M sodium hydroxide.
3. Gently heat the zinc and sodium hydroxide, being careful NOT to boil the solution.
4. Add a penny and simmer until the penny becomes silvery. Flip it occasionally with
tongs.
5. Use tongs to remove the penny from the evaporating dish and rinse it with water.
6. Holding one edge of the penny with tongs, GENTLY heat the penny in a Bunsen
burner until it turns gold. Flip the penny back and forth while heating. You can ruin
your penny by overheating it.
7. Drop the penny in a beaker of water. Remove the penny from the beaker and dry.
Follow-Up Questions
1. What metal made the penny appear silvery?
2. What made the penny appear gold in color?
3. If the penny is heated too strongly it changes back to a copper color. Suggest a
reason for this.
4. If you had actually changed your penny into gold, how much would it be worth? You
may use any means you wish to find the selling price of gold.
5. What is the name given to an alloy made from the two metals found in a penny?
6. Pennies minted prior to 1982 are made from an alloy composed of approximately
98% copper and 2% zinc.
a. Why might a penny be made of an alloy instead of pure copper?
b. If one of these pennies were examined microscopically, it would appear
uniform throughout. Would you predict the penny to be heterogeneous or
homogeneous?
Bonding Unit
Activity #2: Build – a – Molecule
Questions
What do molecules look like?
How can we predict the molecular shapes of molecules?
Objectives
1. Draw Lewis structures for molecules.
2. Construct models to represent the geometrical shapes of molecules.
3. Determine if a molecule is polar or nonpolar.
Introduction
The shape of a molecule greatly affects its properties. In this activity you will use clay
and toothpicks to determine the shapes of the small molecules represented by the
formulas below. You will use toothpicks to represent both bonding pairs and lone pairs
of electrons.
HCN
H2CO
CCl2H2
CO2
O3
H2S
PH3
SF6
Prelaboratory Assignment
1. How do you determine which atom to use as the central atom?
2. How do you find the number of valence electrons for an element?
3. How do you adjust your calculation of electrons for ions with a negative charge?
A positive charge?
4. How many electrons do most atoms desire to reach stability? How many
electrons does hydrogen want to reach stability?
5. Draw Lewis structures for each of the molecules you will build.
Materials
•
•
•
•
Ruler
Protractor
Toothpicks
Modeling clay
Real-World Connections
Ideas behind molecular shape can be connected to:
Smells and scents
Miscibility of liqiuids – “Like dissolves like” refers to the polarity of a molecule
Physical properties of substances such as boiling and melting point
Chromatography
Source:
Adapted from World of Chemistry Lab Generator CD. McDougal Littell
Procedure
1. Use toothpicks and modeling clay to make models for each of the molecules given in
the Prelaboratory Assignment. Make sure the toothpicks stick out an equal distance
from the center clay ball (make sure this distance is the same for all molecules; in this
way we can compare measurements for different molecules). Use plain toothpicks to
represent bonding pairs of electrons between atoms and colored toothpicks for lone
pairs of electrons.
2. Position the atoms and lone pairs of electrons as far apart from each other as
possible.
3. Measure and record the bond angles between the toothpicks.
4. Record the electron pair geometry and shape of each of the molecules.
Cleaning Up
1. Take apart your models. Return all materials as instructed by your teacher.
2. Wash your hands thoroughly before leaving the laboratory.
Analysis and Conclusions
1. Which shape has the longest distance between the ends of the toothpicks? Which
shape has the shortest distance between the ends of the toothpicks?
2. Group together molecules that have the same number of atoms coming off the
central atom. Do these molecules have the same geometry? The same shape?
3. What do the plain toothpicks represent? The colored toothpicks?
4. Why do we position the atoms (clay balls) at the ends of the toothpicks as far apart
as possible?
5. Just by looking at the molecular formula, are you able to predict the shape of a
molecule? Explain.
6. By looking at the geometry of a molecule, how can you determine if it is polar or
nonpolar?
Summary Table
Complete the table below:
Molecule Total number Number of
of atoms and atoms around
lone pairs of central atom
electrons
around
central atom
HCN
O3
CCl2H2
H2CO
H2S
PH3
CO2
SF6
Number of
lone pairs of
electrons
around the
central atom
Molecular
Shape
Polarity
Teacher Notes: Build - A - Molecule Activity
Post lab Discussion
Have the students compare their results. The distances between the ends of the
toothpicks are directly related to the bond angles. The actual distances between the
ends of the toothpicks will differ. However, the HCN model will have the longest
distance since it is linear (180° bond angle).
Make sure the students understand that lone pairs affect the actual bond angles. For
example, H2S, a three atom molecule, has tetrahedral electron pair geometry but a bent
shape with an angle of approximately 109.5°. It is not linear as students might expect
since there are only two atoms bound to the central atom.
HCN
H2CO
CCl2H2
O3
H2S
PH3
Analysis and Conclusions: Answer Key
1. Which shape has the longest distance between the ends of the toothpicks? Which
shape has the shortest distance between the ends of the toothpicks?
The linear shape has the longest distance between the ends of the toothpicks. The
tetrahedral shape has the shortest distance between the ends of the toothpicks.
2. Group together molecules that have the same number of atoms coming off the
central atom. Do these molecules have the same geometry? The same shape?
2 atoms off the central atom: HCN, O3, H2S; 3 atoms: H2CO, PH3; 4 atoms: CCl2H2. The
molecules in a given group do not necessarily have the same electron pair geometry, or
the same shape.
3. What do the plain toothpicks represent? The colored toothpicks?
The plain toothpicks represent bonding electron pairs. Colored toothpicks represent
lone pairs.
4. Why do we position the ends of the toothpicks as far apart as possible?
The toothpicks represent electrons, and electrons are negatively charged and therefore
repel each other. To minimize electron pair interactions, we position the toothpicks as
far apart as possible.
5. Can we use the molecular formula to predict the shape of a molecule? Explain.
We cannot use a molecular formula to predict the shape of small molecules. We need to
also know how many lone pairs of electrons are present (from the Lewis structure) to
determine the shape.
6. By looking at the geometry of a molecule, how can you determine if it is polar or
nonpolar?
Polarity is determined by the symmetry of the molecule. To determine symmetry, look
at the atoms and the lone pairs on the central atom. If there are any lone pairs of
electrons on the central atom, the molecule is polar. If the molecule has the same
atoms around the central atom, then it is nonpolar.
See the next page for the answer key to the chart students fill out during the lab
activity.
Molecule Total number Number of
of atoms and atoms around
lone pairs of central atom
electrons
around
central atom
Number of
Molecular
lone pairs of Shapes
electrons
around
central atom
HCN
2
2
O3
3
2
CCl2H2
4
4
0
H2CO
3
3
0
H2S
4
2
PH3
4
3
1
CO2
2
2
0
SF6
6
6
0
1
2
0
Polarity
Linear
Polar
Bent
Polar
Tetrahedral
Polar
Trigonal
planar
Polar
Bent
Polar
Trigonal
pyramid
Polar
Linear
Nonpolar
Octahedral
Nonpolar
Bonding Unit
Activity #3: Ionic, Covalent, and Metallic Bonding Lab
Question
What physical properties do ionic, covalent, and metallic compounds exhibit?
Materials
NaCl sodium chloride (ionic)
C6H12O22 sugar (polar covalent)
C18H36O6 stearic acid (nonpolar covalent)
Aluminum granules (metallic)
Test tubes
Balance
Bunsen burner
Test tube holder
Small beakers
Stirring rods
Conductivity tester
Mortars and Pestles
Safety Concerns
Wear goggles and lab apron. Avoid contact of all chemicals with eyes and skin. Tell
students to use small amounts of the chemicals for each test. Each lab group should
only need about one gram of each substance, which should be enough to do all of the
tests. When heating the substance, students should hold the mouth of the test tube
away from others. All chemicals in this lab can be disposed of according to Flinn
Suggested Disposal Methods #26a and b. Consult MSDS for any additional safety,
handling, and disposal information.
Real World Connections
Minerals are ionic compounds that are composed of unit cells of specific geometric
shapes.
The understanding of physical properties of specific compounds is the foundation for
development of new materials by scientists and engineers.
Source:
Lab adapted from M. Wiseman, IB Chemistry Teacher
(Website: www.mwiseman.com/courses/chem_ib/) and also Flinn Scientific “Chemtopic
Labs: Chemical Bonding Volume 5”
Procedure
You will conduct tests on each substance to observe the following physical properties:
•
•
•
•
Solubility of the compound in water.
Conductivity of the solid and in aqueous solution. (2 separate solubility tests!)
Melting point
Brittleness
Procedure Help
You can write the procedure to the lab either as separate tests that are organized by
the physical property you are testing, or as one long list of steps. The procedure should
include enough detail that another group could repeat exactly what you did and get
similar results.
Here are some questions to think about as you plan your procedure:
•
•
•
•
Does it matter how much of each substance you use?
What will be the controls in your tests? The variables?
Does the temperature of the flame matter? How can you control it?
Does it matter if you used tap water or distilled water?
Data Collection
As the summary of your observations, complete a data table that organizes the
properties to each general type of compound. You may copy the one below.
Physical
Property
Solubility in
Water
Summary of Results: Properties of Compounds
Ionic
Covalent
Metallic
Conductivity
as a Solid
Conductivity
of Aqueous
Solution
Brittleness
Melting Point
*Remember to look at the grading checklist to ensure that you have included all criteria
as you type your lab report!
Ionic, Covalent, and Metallic Compounds
Formal Lab Grading Checklist
Name(s): ________________________________________ Date: ______
_____
Hr:
Purpose:
• The reason for performing the lab is clear ___
• The purpose is no more than one or two sentences long ___
Materials:
• The materials list is complete ___
• The list includes the size and number of materials used, if applicable ___
Procedure:
• Every step of the experiment is included ___
• The lab could be repeated using only the instructions given ___
• The procedure is written as numbered steps without any pronouns (I, you, we) ___
Results: (Data Table)
• Quantitative data was recorded with units and significant figures ___
• All tables of information are properly labeled ___
• All tables of information are neatly written ___
Summary of Results: (Data Table)
• Describes the properties of ionic and covalent compounds ___
Real-World Connections:
• Describes two practical connections between ionic, covalent, and/or metallic
compounds to our society ___
Overall Appearance:
• The lab is grammatically correct with no spelling mistakes ___
• The lab is organized by the order listed on this grading sheet ___
• The lab is typed ___
Behavior in Lab:
• Volume of voices were low ___
• Focused on completing lab and helping lab partners ___
• Did not bother other groups or engage in disruptive behavior ___
Bonding Unit
Activity #4: Molecular Modeling Lab
Questions
What do molecules look like?
What shapes can molecules form?
How does atomic radius, bond length, and bond strength relate to each other?
Objectives
Since molecules are too small to see, we will be using an online modeling
software program to visualize what these molecules look like and to see the effect of
lone pairs, atomic radius, electronegativity, and multiple bonds on molecular shape and
polarity.
Teacher Notes
A single covalent bond is formed when two atoms share a pair of electrons.
Each atom provides one of the electrons of the pair. If the two atoms are alike in
electronegativity, the bond is said to be nonpolar covalent. If the atoms differ in
electronegativity, the more electronegative element exerts a greater attractive force on
the electrons, and the bond is polar covalent. More than one pair of electrons may be
shared. This results in a double or triple bond.
A group of atoms held together by covalent bonds is called a molecule.
Molecules can be either polar or nonpolar. If all bonds are nonpolar, the molecule is
nonpolar. If the bonds are polar, molecules can still be nonplar if the charge
distribution throughout the molecules is symmetrical. A molecule’s symmetry depends
on its shape, that is, the positions in space of the atoms making up the molecule.
Some possible shapes are linear, bent, trigonal pyramid, tetrahedral, and trigonal
planar. The geometries of a small molecule can be predicted by examining the central
atom and identifying the number of atoms bonded to it and the number of unshared
electrons pairs surrounding it. The shape of the molecule can be predicted using the
VSEPR rule, which states that electron pairs around a central atom will position
themselves to allow for the maximum amount of space between them.
The polarity of a molecule is probably one of the most important properties for
its interaction in the natural world. A dipole is a polar molecule, a molecule where there
is a separation of positive and negative charge. Dipoles attract each other and exert
forces on each other. This is why water is a liquid at room temperature, but carbon
dioxide is a gas.
Real-World Connections
Ideas behind molecular shape can be connected to:
Smells and scents
Miscibility of liquids – “Like dissolves like” refers to the polarity of a molecule
Properties of substances such as boiling and melting point
Chromatography
Source
Jamie Benigna: High School Chemistry Teacher, Roper High School, Birmingham, MI
Procedure
1. Before entering the lab, complete as much of the data table as possible.
a.
b.
c.
d.
Name each compound
Draw the Lewis do structure
Predict the geometry
Predict the polarity
i. If there is no dipole, write “no dipole” in the box
ii. If there is a dipole, draw an arrow to indicate the direction
2. At your computer, access the website
http://cheminfo.chem.ou.edu/~mra/jmol/jmol.php
3. For each of the molecules listed, there is a file under the pull-down menu in the
upper right corner of the screen. The numerical file number is provided under
the formula in your data table. Any molecule with an “x” at the beginning is at
the bottom of the list.
4. Do not worry about recording data in any of the grayed-out boxes.
5. Using the program, investigate each molecule:
a. You can label each element using the “element labels” check box
b. You can spin the molecule by clicking on one of the atoms and dragging it
around
c. You can check the polarity of the molecule using the “molecular dipole”
check box
i. If a dipole is present, a large dipole arrow appears, pointing
towards the direction in which electrons are pulled in the molecule
ii. If no dipole is present, then no arrow is displayed
d. Be sure to check the “multiple bonds” box to check for double and triple
bonds on each molecule
e. To identify bond length:
i. Double-click on one atom
ii. Move the cursor to the atom on the other side of the bond and
double-click again
iii. The bond length will be displayed in nanometers (nm)
f. To identify bond angle:
i.
ii.
iii.
iv.
v.
Double-click on one of the outside atoms
Move the cursor and click once on the central atom
Move the cursor and double-click on a different outside atom
The bond angle will be displayed on the model
If the molecule is not symmetrical, try checking all of the bond
angles – they might not all be equal!
Name
Beryllium
Chloride
Formula
Lewis Dot
Structure
Molecular
Shape
Molecular
Polarity
Bond
Lengths
Bond
Angle
BeCl2
I.A.1.BeCl2
O2
O-O
VI.A.2.o2
N2
N-N
xN2
CH4
Chloromethane
VI.B.3.ch4
CH3Cl
C-H
H-C-H
Formaldehyde
VI.B.4.ch3cl
H2CO
C-Cl
C-O
Cl-C-H
H-C-H
XH2CO
CO2
C-H
O-C-H
B-F
F-B-F
B-Cl
Cl-B-F
VI.A.4.co2
H2 O
VI.B.1.h2o
BF3
VI.C.bf3
BF2Cl
VI.C.4.bf2cl
NH3
VI.C.2.nh3
C2H6
Ethene
II.A.1.ch3ch3
C2H4
II.A.2.ch2ch2
Ethyne
C2H2
II.A.3.chch
C-C
C=C
Analysis and Conclusion Questions
1. Can a molecule with nonpolar bonds ever be polar? Why or why not?
2. Can a molecule with polar bonds ever be nonpolar? Why or why not?
3. What is a dipole?
4. List the five different molecular geometries we will encounter in this lab and
indicate the bond angles for each.
5. Does there appear to be a correlation between molecular geometry and polarity?
Do you notice a pattern between symmetry of a molecule and polarity?
6. Did the bond angles from the software differ from those you had predicted?
(Look at BF2Cl, H2CO, and CH3Cl) Why might this occur?
7. Looking at the last three molecules, does your data support the idea that triple
bonds are shorter than double bonds, which are shorter than single bonds? Why
or why not?
8. Looking at the first two molecules, explain why N2 has a shorter bond length
than O2, even though oxygen has a smaller atomic radius.
9. The polarity of a substance can have a great effect on its reactivity and
solubility. A rough rule for solubility is “like dissolves like.” Knowing the general
rule, what can you predict about the polarity of alcohol if you know that alcohol
dissolves in water? Why do you think that dry cleaners do not use water or
alcohol to dissolve greasy stains?
Bonding Unit
Activity #5: Polarity Stations
Question
How can we explain interactions of matter by the concept of polarity?
Objective
Explain interactions of matter by using the concepts of polarity, as well as density,
bonding, and molecular geometry.
Materials
Station 1: Bending Water – balloons, water
Station 2: Floating Chads – chads from an index card with one side blackened with a
pencil, large Erlenmeyer flask, about 1 -2 inches depth of hexane and water
Station 3: Mini Lava Lamp – Pre-form 2L bottle, pop bottle screw cap, mineral oil,
water, food coloring, glitter (optional)
Station 4: Liquid Art – Petri dish, milk, food coloring, dish soap, beaker, toothpick
Station 5: Magic Salt – balloon, salt
Station 6: Magic Sand – Regular and Magic sand, water, 2 beakers, spoon, tub for
“used” sand
Station 7: Stain remover – turpentine, kerosene, alcohol, water, used motor oil, strips
of cloth,
Station 8: Penny Stacker – pennies, water, alcohol
Safety Concerns
Hexane is flammable! Keep away from flame and heat. Store volatile liquids in the
fume hood to evaporate. Liquids can be used again for the lab the following year.
Refer to MSDS and Flinn Suggested Disposal Methods for additional information on
safety, handling, and disposal methods
Source
Tracy Veresh, Ferndale High School, Ferndale, MI and
Janet Lucius, Rochester High School, Rochester, MI
Station Directions
Station 1: Bending Water
USES BALLOONS—stay away if you have a latex allergy!
1. Run a small stream of water under the faucet.
2. Place the “unrubbed” balloon near the stream. Do you notice anything
occurring?
3. Rub the FACE side of the balloon vigorously against your clothes or in your hair
and bring it close to, but not touching, the stream of water. In order to charge
the balloon, the hair it is rubbed on must be clean (not oily), and product-free.
Station 2: Floating Chads
1. Observe the contents of the flask.
2. After making CERTAIN that the flask is tightly stoppered, GENTLY tilt the flask
back and forth.
Station 3: Mini Lava Lamp
1. Fill 1/3 of a 2-L pre-form mini bottle with water, and 2/3 with mineral oil.
2. Add a couple of drops of food coloring and a pinch of glitter, if desired.
3. Screw on the top of the mini bottle and shake gently
4. You may take this science project with you!
Station 4: Liquid Art
1. Pour milk into the Petri dish so it is about half full. Place two drops of each color
of food coloring into the milk. The drops can be place at 12, 3, 6, and 9, as if
you were looking at the face of a clock.
2. Place a small drop of soap into the center of the Petri dish using the toothpick.
3. After you are finished, pour the liquids in the pie tin down the sink. Rinse out
the Petri dish with water.
Station 5: Magic Salt
1. Locate the plate with table salt (NaCl) on it.
2. Rub the FACE side of the balloon vigorously in your hair or on your clothes. If
you use the hair, the hair must be clean and product-free.
3. Gradually bring the FACE side of the balloon closer to the salt.
4. Wipe off the salt with a paper towel.
Station 6: Magic Sand
1. Fill up two beakers about half-way with water.
2. To the first beaker, add a couple of spoonfuls of magic sand. To the second
beaker, add a couple of spoonfuls of regular sand.
3. Stir each mixture with a spoon.
4. When you are finished with your observations, pour off as much water as
possible into the sink. Then dump the regular sand into the designated tray.
Scoop the magic sand back into the labeled beaker.
Station 7: Stain Remover
Part 1
1. Place 20 drops of turpentine and 20 drops of kerosene in a test tube.
2. Swirl gently. Are they miscible?
3. Pour results into waste jar. Nothing goes down the drain!
4. Next, place 20 drops of kerosene and 20 drops of water in a test tube.
5. Swirl gently. Are they miscible?
6. Pour results into waste jar. Nothing goes down the drain!
Part 2
1. Obtain 4 pieces of cloth.
2. Label each square with one of the following letters:
a. Alcohol
b. Turpentine
c. Kerosene
d. Water
3. Lay out the 4 squares with paper towel under them at your lab station.
4. Place one drop of used motor oil on each square cloth.
5. Directly on top of the motor oil on each square cloth.
6. Directly on top of the motor oil, place 10 drops of one of the substances listed
above. (Example, put 10 drops of alcohol on the square labeled “a”)
7. Allow each square to sit for 5 minutes.
8. Scrub each square thoroughly under running water for 30 seconds.
9. Spread each square out on the lab table.
10. Rank your substances 1-4 based on the effectiveness of how well the stain was
removed.
11. Throw the squares in the trash.
Station 8: Penny Stacker
1. Place two pennies on the paper towel.
2. On one penny, count how many drops of oil fit on the penny before the oil spills
onto the paper towel.
3. On the other penny, count how many drops of water fit on the penny before the
water spills onto the paper towel.
Questions and Conclusions for Polarity Stations
Station 1: Bending Water
1. Sketch the behavior of the water with the balloon.
2. By charging the balloon you are collecting electrons on the side of the balloon that
was rubbed. Use this information, along with the fact that water is a polar
molecule, to explain which part of the water molecule is attracted to the balloon.
Use can use words or draw, but both explanations should include knowledge about
the polarity of a water molecule.
Station 2: Floating Chads (Chads—you know, the hole punched out of paper
in a hole punch)
1. Is the substance in the flask composed of multiple layers? __________________
2. Describe the orientation of the chads in the Erlenmeyer flask. Which liquid is the
grey side facing? Which liquid is the white side facing?
3. Can you get the chads to flip over (change orientation) and stay that way? If so,
you must show me.
4. The chads are pieces of paper covered in pencil, which is actually just graphite
composed of carbon-carbon bonds. Now that you know the gray side of the chads
are covered in carbon-carbon bonds (hmmm…what kind of bond type is that?),
explain what is going on at the molecular level. FYI: One layer of the substance
in the flask is hexane, the other layer is water.
Station 3: Mini Lava Lamps
1. After you shake the contents of the mini bottle, what do you observe?
2. Which liquid does the food coloring mix with? Why do you think it only mixes with
this substance?
3. Based on your knowledge of polarity and density, explain the interaction between
the mineral oil and water.
Station 4: Liquid Art
1. Describe the interaction between the food coloring and milk.
2. Describe the interaction of the food coloring and milk once the soap has touched the
surface.
3. After mixing, do the substances remain mixed? .
4. Give an explanation to why this phenomenon occurs.
Station 5: Magic Salt
1. Use a picture or words to describe the interaction between the salt and the charged
balloon.
2. Is salt a covalent or ionic compound? Based on this information (and the fact that
by rubbing the balloon you collected electrons on the face side of the balloon), why
would this interaction occur? Which end of the NaCl compound is attracted to the
charged balloon?
Station 6: Magic Sand
1. Describe the difference between the interactions of water and the two types of
sand.
2. Explain how you think magic sand works.
3. Describe a way that you could possibly make your own magic sand.
Station 7: Stain Remover
1. Which substances were miscible? Which were immiscible?
2. Which solvent removed the oil stain the best? Explain why this solvent worked the
best by the concept of polarity.
Station 8: Penny Stacker
1. How many drops of oil fit on the penny? How many drops of water?
2. Why were you able to fit more drops of __ on the penny than drops of ___? Your
response should include the concept of “hydrogen-bonding”.
Bonding Unit
Activity #6: Polar Bears and Penguins
Questions
What is polarity?
How do you determine the polarity of molecules?
How does polarity relate to electronegativity?
How do you determine which end is positive and negative in polar molecules?
Objective
In this lesson you will be exploring polarity and bonding between atoms in greater
detail. A comic book will provide new information about these topics and will introduce
you to the concept of electronegativity, which helps us to understand partial charges.
Teacher Notes
For more informational background and detailed lesson plan see the following website
from Key Curriculum Press, “Living by Chemistry” series.
http://www.keypress.com/x7785.xml (Click on “Sample lesson – Teacher)
Source
Stacy, Angelica. LHS Living By Chemistry. Emeryville, CA: Key Curriculum Press, 2006.
Website: http://www.keypress.com/x10.xml
Questions to answer
Use the cartoon called “The Bare Essentials of Polarity” to answer the following
questions.
1. How does the comic book define a “polar molecule?”
2. Define electronegativity as you understand it, after reading the first two pages of
the comic book.
3. Interpret the picture at the bottom of page 1. Explain how the iceberg,
penguins, and polar bears represent trends in electronegativity.
4. What is the artist trying to represent when there are two polar bears arm
wrestling together or two penguins arm wrestling together?
5. What three types of bonds are represented on page 3 of the comic book? What
happens to the bonding electrons in each type of bond?
6. Explain why there are four scoops of ice cream in the illustration of O2 on
page 3.
7. What do the six scoops of ice cream represent in the illustration of N2 on page 4?
8. Describe what you think is happening to the penguin in the CO2 molecule in the
picture on page 4.
9. Name three things that the picture of CO2 on page 4 illustrates about the
molecule.
10. Describe what you think is happening to the penguins in the illustration of H2O
on page 4.
11. Explain what you think the crossed arrow represents in the comic book.
12. What are the two definitions of “dipole” given in the comic book?
Making sense
What does electronegativity have to do with polarity?
If you finish early…
Using polar bears and penguins create an illustration showing a hydrogen sulfide
molecule, H2S. (Hint: You may wish to start with a Lewis dot structure.)
Bonding Unit
Teaching Tools: Covalent Bonds and Polarity
Purpose
This demonstration is used to help visualize a polar versus nonpolar covalent bond.
Construction
Straighten a large paper clip. Pass it through the centers of two Styrofoam balls. Bend
a hook at one end of the wire, slide the balls onto the hook, bend a hook at the other
end of the wire close to the ball, and cut off the excess wire. Find two identical rubber
bands, and attach one to each hook. As the balls will represent electrons, you might
wish to draw minus signs on each. Prepare a second identical model, except that one
rubber band must be strong and one must be weak, but the same length.
Procedure
To demonstrate a nonpolar covalent bond, mark the back of each hand with an “H”.
Grasp each rubber band of the first model (the one with identical rubber bands) with
one finger, and pull to stretch the rubber bands. Notice that the “electrons” are
attracted equally by both atoms.
To demonstrate a polar covalent bond, mark the back of your right hand with “H” and
the back of your left hand with “F”. Grasp the second model so that the weaker rubber
band is held by the right “H” hand and the stronger rubber band is held by the left “F”
hand. Notice that when you pull to stretch the rubber bands, the “electrons” are pulled
closer to the F atom.
You may want to point out the limitations of the model; the chemical bonds result from
electrical attraction (not rubber bands) and that the electrons are constantly moving at
a high speed in random motion. The model is not to scale.
Source
Guenther, Al. Practical Activities for Strengthening Your Teaching of Chemistry Concepts
in Your Science Classes. Bellevue: Bureau of Education and Research, 2003.
Bonding Unit
Bond Length and Strength: Discussion Questions
Refer to Figure 1 for questions 1-3.
1. Which type of bond is the strongest: single, double, or triple bonds? Describe what
you think may affect how strong a bond is between atoms.
2. Which type of bond is the longest: single, double, or triple bonds? Describe what
you think may affect the length of bond between atoms.
3. State the relationship between bond strength and bond length. List any exceptions
that you see.
Refer to Figure 2 for questions 4 and 5.
4. What type of bond is stronger, ionic or covalent bonds?
5. Describe the relationship between the charge of the ion and strength of bond in
ionic compounds.
FIGURE 1
FIGURE 2
Reference Charts and Diagrams
Electronegativity Chart
Molecular Shapes
Bonding Unit
Worksheet: Lewis Structures, VSEPR, Polarity, IM Forces
For each of the following molecules, draw the Lewis structure (with any resonance
structures, if applicable), indicate the molecular shapes, indicate the molecular polarity
(if any), and identify the major intermolecular force in each compound.
1)
carbon tetrafluoride
2)
BF3
3)
NF3
4)
H2CS
5)
carbonate ion
6)
CH2F2
7)
nitrate ion
8)
O2
9)
PF3
10)
H2S
Answer Key: Lewis Structures, VSEPR, Polarity, IM Forces For each of the following molecules, draw the Lewis structure (with any resonance
structures, if applicable), indicate the molecular shapes, indicate the molecular polarity
(if any), and identify the major intermolecular force in each compound.
1)
carbon tetrafluoride
2)
BF3
3)
NF3
4)
H2CS
5)
carbonate ion
6)
CH2F2
7)
nitrate ion
8)
O2
9)
PF3
10)
H2S
Worksheet: Creative Compounds
1)
List three covalent objects that can be found in this classroom:
a) __________________ b) __________________ c) ____________________
2)
Haikus are three line Japanese poems where the first line has five syllables, the
second has seven syllables, and the third has five syllables. Write a haiku about
how the electrons behave when a covalent compound is formed.
3)
Describe several tests you could conduct to determine whether a compound is
ionic or covalent.
4)
Write the names of everyday objects that have the same shapes as the following
molecular shapes.
linear: ________________________________________________
bent: ________________________________________________
trigonal pyramidal: ____________________________________________
trigonal planar: ______________________________________________
tetrahedral: ________________________________________________
5)
If you were a chemical, would you want to be ionic or covalent, and why?
1)
Answer Key: Creative Compounds
List three covalent objects that can be found in the sinks in this classroom:
Any three covalent compounds would be fine. Common things include
soaps, sponges, paper towels, pencils, pens, and other covalent
objects.
2)
Haikus are three line Japanese poems where the first line has five syllables, the
second has seven syllables, and the third has five syllables. Write a haiku about
how the electrons behave when a covalent compound is formed.
As long as the poem is three lines long with the correct number of
syllables and emphasizes that covalent bonds involve the sharing of
electrons, give this credit.
3)
Describe several tests you could conduct to determine whether a compound is
ionic or covalent.
Covalent compounds could be liquids or gases; ionic are solids at room
temperature. Covalent compounds are usually softer, whereas ionic
compounds are brittle. Ionic compounds have higher melting and
boiling points. Ionic compounds dissolve in water and are electrolytes.
4)
Write the names of everyday objects that have the same shapes as the following
molecular shapes.
linear: baseball bat, golf club, pencil, pen, etc.
bent: boomerang, barbecue tongs, forceps, etc.
trigonal pyramidal: be generous when giving credit for this one, as there
really aren’t very many trigonal pyramidal objects in everyday use.
trigonal planar: Mercedes hood ornament, etc.
tetrahedral: some jacks, pyramids, etc.
5)
If you were a chemical, would you want to be ionic or covalent, and why?
You will get some very peculiar answers for this one!
Source
Guch, "Covalent Compound Scavenger Hunt." Worksheet Involving Ionic and Covalent Compounds. 27
Jun 2008 <http://misterguch.brinkster.net/ioniccovalentworksheets.html>.